How to render Wireframe for the entire scene not just one object?
Here how would I do this task.


Get 2.8x version
Set up overlays like this:





When setup matcap and cavity as you want:







If the result is not bad, click View -> Viewport render.
If you want wireframe on top of Cycles (or outer) Render Setup viewport like this:







In color management set View transform to default 





When  click View -> Viewport render and compose resulted image over render using multiply.